Silo-fodder or silage is generally produced by fermenting a suitable vegetable matter, such as husks or hay, in the presence of lactic acid in a silo. It is desireable that fermentation of the vegetable matter takes place in a substantially oxygen free atmosphere to prevent rotting.
Two types of silos are commonly employed in the production of silo-fodder. These may be termed as hopper-type silos and trench silos. The former is in the nature of a raised sheet metal structure adapted for top end loading and low level withdrawal. While such a silo may be made airtight to allow for oxygen-free fermentation, the cost of the silo is relatively high and special silo loading equipment is required.
The trench silo normally takes the form of an elongated trough of general U-shaped section. The trough may be located at ground level, or may be wholly or partially sunken into the ground. During the production of silo-fodder, the trough is covered by one or more plastic sheets. This arrangement offers the advantages of relatively low construction costs, and easy loading and compacting by means of common farm implements such as tractors. However, no effective protection is given against free oxygen, resulting in considerable losses due to rotting.